Abstract
BackgroundPoor adherence to isoniazid (INH) preventive therapy (IPT) is an impediment to effective control of latent tuberculosis (TB) infection. TB patients who smoke are at higher risk of latent TB infection, active disease, and TB mortality, and may have lower adherence to their TB medications. The objective of our study was to validate IsoScreen and SmokeScreen (GFC Diagnostics, UK), two point-of-care tests for monitoring INH intake and determining smoking status. The tests could be used together in the same individual to help identify patients with a high-risk profile and provide a tailored treatment plan that includes medication management, adherence interventions, and smoking cessation programs.Methodology/Principal Findings200 adult outpatients attending the TB and/or the smoking cessation clinic were recruited at the Montreal Chest Institute. Sensitivity and specificity were measured for each test against the corresponding composite reference standard. Test reliability was measured using kappa statistic for intra-rater and inter-rater agreement. Univariate and multivariate logistic regression models were used to explore possible covariates that might be related to false-positive and false-negative test results. IsoScreen had a sensitivity of 93.2% (95% confidence interval [CI] 80.3, 98.2) and specificity of 98.7% (94.8, 99.8). IsoScreen had intra-rater agreement (kappa) of 0.75 (0.48, 0.94) and inter-rater agreement of 0.61 (0.27, 0.90). SmokeScreen had a sensitivity of 69.2% (56.4, 79.8), specificity of 81.6% (73.0, 88.0), intra-rater agreement of 0.77 (0.56, 0.94), and inter-rater agreement of 0.66 (0.42, 0.88). False-positive SmokeScreen tests were strongly associated with INH treatment.ConclusionsIsoScreen had high validity and reliability, whereas SmokeScreen had modest validity and reliability. SmokeScreen tests did not perform well in a population receiving INH due to the association between INH treatment and false-positive SmokeScreen test results. Development of the next generation SmokeScreen assay should account for this potential interference.
Highlights
In 2010 alone, there were an estimated 8.8 million incident tuberculosis (TB) cases and 1.5 million TB-related deaths globally [1]
Adherence is major concern with treatment of latent TB infection (LTBI) which has a much more prolonged treatment period, typically nine months of isoniazid (INH), which often results in lower treatment completion rates
There have been three recent systematic reviews that have shown that smoking is an independent risk factor for TB infection, TB disease, and TB mortality [3,4,5]
Summary
In 2010 alone, there were an estimated 8.8 million incident tuberculosis (TB) cases and 1.5 million TB-related deaths globally [1]. Adherence is major concern with treatment of latent TB infection (LTBI) which has a much more prolonged treatment period, typically nine months of isoniazid (INH), which often results in lower treatment completion rates. Some studies suggest that adherence rates are lower in TB patients who smoke [2,3,4,5,6,7]. Poor adherence to isoniazid (INH) preventive therapy (IPT) is an impediment to effective control of latent tuberculosis (TB) infection. TB patients who smoke are at higher risk of latent TB infection, active disease, and TB mortality, and may have lower adherence to their TB medications. The tests could be used together in the same individual to help identify patients with a high-risk profile and provide a tailored treatment plan that includes medication management, adherence interventions, and smoking cessation programs
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